KR20160048957A - Water-based cathode slurry for a lithium ion battery - Google Patents

Abstract

According to the present invention, there is provided an aqueous lithium ion battery cathode slurry comprising a cathode active material containing a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder comprises an aggregate of primary particles and the primary particles comprise a polymer Thereby forming a coating layer. The polymer is preferably a fluorine-containing polymer containing 50 wt% or more of fluorine. The coating layer preferably comprises a first coating inner layer and a second coating outer layer, the second outer layer comprises a fluorine containing polymer, and the first inner layer comprises the reaction product of the fluorine containing polymer and the primary particle surface. The reaction product preferably includes LiF.

Description

[0001] Description [0002] WATER-BASED CATHODE SLURRY FOR A LITHIUM ION BATTERY FOR LITHIUM ION BATTERY [0003]

The present invention relates to an aqueous electrode coating technique for a positive electrode of a lithium ion rechargeable battery.

A lithium ion battery is basically a jelly roll impregnated with an electrolyte, attached to a current connector, and inserted into a battery case. The jelly roll comprises at least a cathode (anode), a porous electrically insulating film (separator) and a cathode (cathode). Typically, the electrode is a metal foil (or substrate) coated on both sides with an electroactive mixture. The electroactive mixture comprises a conductive agent that is porous and consists of particles of active material and includes a binder that bonds the particles to one another and adheres to the substrate and increases conductivity. After battery assembly, the pores will be filled by the electrolyte.

The anode (anode) typically consists of a copper foil as a current collector, the active additive typically consists of> 90% graphitic carbon, and the remaining <10% consists of a binder and a conductive agent.

Conventional electrode manufacturing technology is a wet coating process for coating a viscous slurry onto a collector substrate. In a conventional approach, the slurry is an NMP (N-methyl-pyrrolidone) organic solvent dispersion. A binder, typically a PVDF (polyvinylidene fluoride) based copolymer, is not only dissolved in the solvent and in the conductive agent. The electroactive electrode material is suspended in the slurry.

NMP / PVDF based slurries have excellent viscoelastic properties that enable high quality industrial coatings, typically at high coating speeds of several kilometers per hour.

PVDF is not the best binder but is well suited for organic NMP based coating technology. An important aspect of PVDF as a binder is its ability to swell. The electrolyte used in the battery is not capable of dissolving the PVDF binder but can soften it. As a result, "swollen" PVDF has Li ion conductivity. After the electrode is dried, a portion of the active material particles is coated with PVDF. If PVDF is not an ionic insulator, the surface coating will block lithium migration. Due to the ionic conductivity of the swollen polymer, excellent capacity and rate-limiting characteristics are achieved in PVDF coating. NMP is flammable and has some toxicity. NMP vapors are a major concern due to the risk of inhalation and explosion, and can not be released to the environment in large quantities.

Conventional organic coating processes, i.e. coating of NMP / PVDF based slurries on current collector substrates, are expensive. Since NMP has a relatively high vapor temperature, electrode drying is performed at relatively high temperatures (e.g., 120 占 폚). For cost and environmental reasons, the NMP must be recycled from the hot dry gas. Recycling can be done by condensation, but requires energy and relatively expensive equipment. Flammability of NMP requires explosion safety equipment, which further increases the cost. Accordingly, attempts have been made to replace the organic NMP substrate coating process with an aqueous coating process. This attempt was completely successful for the cathode (anode). A decade ago, the anode was only coated by the NMP process, but most of the current anode is now produced by an aqueous coating process. Advantages of the aqueous coating process are: (a) non-flammability - no need for its explosion-proofing device, (b) low drying temperature, and (c) solvent recycling is unnecessary.

A typical aqueous slurry for anode coating is prepared as follows. CMC (carboxymethylcellulose) is dissolved in water to improve the viscous mechanical properties that enable industrial coating operations. At the same time, CMC serves as a carbon electroactive material based on graphite and as a surfactant for the carbon conductive agent. After electrode drying, CMC remains and acts as a binder, but CMC is brittle. SBR (styrene-butadiene rubber) microparticles as a binder are added to the slurry to soften the electrode, make the electrode more elastic, and improve the adhesion between the substrate and the coating layer. The binder particles are not dissolved. The advanced SBR latex binder can be obtained from JSR Corporation (Tokyo, Japan).

In the case of a cathode (cathode), a similar approach is preferred. Similar to the anode technology, in the case of cathodes, aqueous coatings will save money and be more environmentally friendly. However, as opposed to the anode, the aqueous coating of the cathode is more difficult. The main problem is the fact that many cathode materials are not inert in water, causing problems and complicating the aqueous coating process of the cathode. Examples of the use of aqueous coating techniques for making cathodes can be found in U.S. Patent No. 2013-0034651. Within the battery, the cathode is a high voltage (as measured against Li / Li +). Rubber is stable at low anode voltage, but at high voltage most rubber decomposes. Thus, more suitable rubbers, for example fluorinated acrylic latex rubbers, have been developed. One such binder is Fluorine Acrylic Hybrid Latex (TRD202A), supplied by JSR Corporation. In the specification, the present inventors refer to as "Fluorine Acrylate Polymer (FAP) ".

In WO2012-111116, there is provided a lithium ion secondary battery having an anode formed of an active material and a binder in an aqueous solvent. The surface of the cathode active material is coated with a hydrophobic coating and the binder is dissolved or dispersed in an aqueous solvent. The cathode active material powder has secondary particles in a range of approximately 1 m to 15 m, and is formed by agglomeration of the active material of a plurality of fine particles. The positive electrode active material coated with the water-repellent resin can be obtained by dispersing or mixing the material and the water-repellent resin such as PVDF in a suitable solvent to prepare a paste-like mixture and drying the paste-like mixture at 100 ° C to 180 ° C. This approach is not new and is for other reasons, but has already been described in WO2009-097680. The present inventors have found that the coatings obtained by the processes of WO2012-111116 and WO2009-097680 are not very satisfactory to solve the problem to be solved. Sufficient protection of the cathode surface from complete coating or water penetration, or satisfactory adhesion of the coating layer to the cathode material is not achieved. What is achieved is only a partial coating with a relatively thick and poorly adhering polymeric layer that does not penetrate the grain boundaries, so that only a fraction of the secondary particles are protected and the primary particles are not protected. This has been described in considerable detail in WO2011-054440.

In the future, the lithium battery market is expected to become increasingly dominant in automotive applications. Automotive applications require very large batteries. Batteries are expensive and must be produced at the lowest possible cost. Much of the cost comes from the anode. Providing these electrodes by cheap and environmentally friendly processes can help to reduce costs and increase market acceptance. Therefore, aqueous coating technology is an advantage for developing the lithium battery market for automotive applications. In addition, automotive batteries must last for many years. During this time the battery does not always work. The long service life of a battery is related to two characteristics: (a) low loss of capacity during storage and (b) high cycle stability. Many automotive batteries, especially hybrid automotive batteries, require high pulse power to enable efficient regenerative braking as well as to provide sufficient power during acceleration.

An important characteristic associated with pulse power is direct current resistance (DCR). Low DCR resistance is essential to achieve high pulse power. In the past, there has been a problem in improving the DCR resistance of a cathode made by an aqueous electrode coating process. In addition, there was a problem in limiting the increase in DCR during long-term operation of the battery.

It is an object of the present invention to provide an anodic aqueous coating composition particularly suited for such automotive battery applications, especially in terms of the DCR problems cited above.

In a first aspect, the present invention is an aqueous lithium ion battery cathode slurry comprising a cathode active material comprising a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder comprises an aggregate of primary particles, Wherein the water soluble lithium ion battery cathode slurry comprises a coating layer comprising a polymer. The coating layer may have hydrophobicity. The polymer may be a fluorine-containing polymer comprising 50 wt% or more of fluorine.

In one embodiment, the coating comprises a first coating inner layer and a second coating outer layer, the second outer layer comprises a fluorine containing polymer, and the first inner layer comprises a reaction product of a fluorine containing polymer and a primary particle surface . The present invention also relates to an aqueous lithium ion battery cathode slurry comprising a cathode active material comprising a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder comprises an aggregate of primary particles and the primary particles comprise a polymer Comprising a fluorine containing polymer wherein the polymer comprises at least 50 wt% of fluorine, the coating layer comprising a first coating inner layer and a second coating outer layer, the second outer layer comprising a fluorine containing polymer , Wherein the first inner layer comprises a reaction product of a fluorine-containing polymer and a primary particle surface.

In this embodiment, the reaction product may comprise LiF. Lithium in LiF can originate from the primary particle surface. Among the reaction products containing LiF, fluorine may be derived from the partially decomposed fluorine-containing polymer present in the second outer layer. In one embodiment, the first coating inner layer comprises a LiF film having a thickness of at least 0.5 nm, preferably at least 0.8 nm, and most preferably at least 1 nm. In some embodiments, the fluorine containing polymer may be one of PVDF, PVDF-HFP, or PTFE, and the fluorine containing polymer preferably consists of agglomerated primary particles having an average particle size of from 0.2 μm to 0.5 μm.

In one embodiment combined with this embodiment, the lithium transition metal oxide has the general formula Li _{1 + a} M _1-a O _{2 + b} M ' _k Sm, wherein -0.03 <a <0.06 and b M is at least one element selected from the group consisting of Ni, Mn, Co, Mg and Ti, and M 'is at least one element selected from the group consisting of Ca, Sr, Y, La, Ce and Zr, where 0? K? 0.1, where k represents wt% and 0? M? 0.6, where m represents mol%. Where x> 0, y> 0, z> 0, x + y + z = 1, and x / y≥1, where M = Ni _x Mn _y Co _z . In one embodiment, 0.33? X? 0.7 and 0.1 <z <0.35. In another embodiment, 0.4? X? 0.6 and x / y> 1. In another embodiment, k = m = 0, 0? A? 0.04, x + y + z = 1, 0.4? X? 0.6, x / y> 1 and 0.1 <z <0.35.

It is clear that another embodiment of the product according to the present invention may be provided having the characteristics included by the embodiment of the different products described above. The aqueous slurry may further comprise a conductive agent (e.g., Super-P or graphite) and an aqueous binder (e.g., carboxymethylcellulose (CMC) or fluorine acrylate polymer (FAP) have.

In a second aspect, the invention is directed to the use of an aqueous lithium ion battery cathode slurry of one of the embodiments described above in the production of a cathode for a lithium ion battery, wherein said cathode comprises an aluminum substrate Can be used. The present invention may also provide the use of an aqueous lithium ion battery cathode slurry of one of the embodiments described above in the manufacture of lithium ion batteries for automotive applications.

The present invention discloses a Ni-Mn-Co or NMC-based cathode material coated with a double shell for application to aqueous coatings. The outer shell is a polymer and the inner shell is a LiF thin film. Such materials are known from WO2011-054440 in which the structure, advantages, and methods for making the same are discussed in detail. Therefore, the above application is incorporated herein by reference in its entirety. The outer shell increases the water stability of the cathode material. The less surface coating in water will be associated with less damage to the cathode and less ion exchange and will be discussed in more detail below, but since ion exchange causes pH increase of the slurry and strong pH recovery, It is not preferable. The inner shell is LiF and is derived from the reaction between the polymer and the residual base present on or near the surface of the cathode material. The reaction effectively decomposes the surface base thereby reducing the base potential of the cathode material. In WO2011-054440, a double-shell coated active material is proposed for a conventional NMP (N-methyl-pyrrolidone) organic solvent-based dispersion. The patent relates to the absorption of water vapor and CO ₂ from the surroundings by exposure of the material to air between sintering and incorporation of the powder during storage at electrodes in a battery manufacturing plant. Since the reaction caused by direct immersion in the aqueous binder solution is a slightly different characteristic and more intense, it has not been possible to conclude from the above-described air exposure test in connection with use with an aqueous substrate binder. Indeed, one of the main causes of the performance degradation of batteries with aqueous substrate binders in direct contact with the lithium transition metal powder is the damage of the cathode causing unwanted side reactions in the battery. This is M. Are identified in M. Spreafico et al., "PVDF Latex As a binder for Positive Electrodes in Lithium-Ion Batteries &quot;, in Industrial & Engineering Chemistry Research, published on the internet on February 18, Sprea Pico states that water can progressively damage the particle surface, thereby catalyzing side reactions from the cathode, promoting irreversible reactions, and causing loss of capacity during cycling.

Fig. 1a: Rate-of-property results of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1b: Temperature characteristics of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1c: DCR results of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1d: Results of DCR increase of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1e: Recovery capacity results of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1f: Retention capacity results of NMC532 coated with aqueous binder (full cell of NMP substrate binder)
Figure 1g: Cycle stability results of NMC532 coated with aqueous binder at room temperature (full cell of NMP substrate binder)
(Fig. 1h): Cycle stability results of NMC532 coated with aqueous binder at 45 DEG C (full cell of NMP substrate binder)
[Figure 2a]: Rate characteristic results of NMC532 in NMP substrate binder system and aqueous binder system
Figure 2b: DCR of NMC532 in NMP substrate binder system and aqueous binder system
Figure 2c: DCR increase of NMC532 in NMP substrate binder system and aqueous binder system
Figure 2d: The retention capacity of NMC532 in the NMP substrate binder system and aqueous binder system
Figure 2e: Recovery capacity of NMC532 in NMP substrate binder system and aqueous binder system
[Figure 2f]: Cycle stability results of NMC532 at room temperature in NMP substrate binder system and aqueous binder system
[Fig. 2g]: Cycle stability results of NMC532 at 45 [deg.] C in an NMP substrate binder system and an aqueous binder system
[Figure 3a]: The rate-limiting characteristic results of NMC532 in NMP substrate binder system and aqueous binder system
Figure 3b: Temperature characteristics of NMC532 in NMP substrate binder system and aqueous binder system
Figure 3c: DCR of NMC532 in an NMP substrate binder system and an aqueous binder system
[Figure 3d]: Increase in DCR of NMC532 in NMP substrate binder system and aqueous binder system
Figure 3e: The retention capacity of NMC532 in an NMP substrate binder system and an aqueous binder system
Figure 3f: Recovery capacity of NMC532 in NMP base binder system and aqueous binder system
[Figure 3g]: Cycle stability results of NMC532 at room temperature in an NMP substrate binder system and an aqueous binder system
[Figure 3h] Cycle stability results of NMC532 at 45 [deg.] C in an NMP substrate binder system and an aqueous binder system
4: FESEM micrograph of Li Ni-Mn-Co oxide / 1% PVDF mixture heated at 250 ° C
Figure 5a: SEM micrographs of the coated electrode (not compressed with a roll press)
Left: aqueous coating - no acid added. Right: acid addition
[Figure 5b]: Comparison of pH after equilibration, after one minute of acid addition for four different samples and after two hours of acid addition.
Figure 6a: Rate characteristics of NMC532 and dual shell NMC532 in a full battery of aqueous binder system
Figure 6b: Temperature characteristics of NMC532 and dual shell NMC532 in a full cell of an aqueous binder system
Figure 6c: DCR of NMC532 and dual shell NMC532 in a full cell of an aqueous binder system
[Figure 6d]: DCR increases in NMC532 and double shell NMC532 in a full cell of an aqueous binder system
[Figure 6e]: The retention capacity of NMC532 and double shell NMC532 in a full cell of an aqueous binder system
[Figure 6f] Recovery capacity of NMC532 and double shell NMC532 in a full cell of an aqueous binder system
[Figure 6g] Cycle stability (full cell of aqueous binder) at room temperature of NMC532 and double shell NMC532
(Fig. 6h): Cycle stability (full cell of aqueous binder) of NMC532 and dual shell NMC532 at &lt; RTI ID =

The cathode of interest is a Ni-Mn-Co or NMC based cathode material. These general compositions are Li [Li _x M _{1 -x} ] O _{2 wherein} M is Ni _{1 -a b} Mn _a Co _b . The present inventors will refer to the lithium oxide composition as "NMC" in the future. M can be doped up to 5 mol% by dopant A and dopant A can be doped with Mg, Al, Ti, Zr, Ca, Ce, Cr, W, Si, Fe, Nb, And &lt; RTI ID = 0.0 &gt; B, &lt; / RTI &gt; A known example is a "111" compound with a = b = 0.33 resulting in a = 0.30, b = 0.20 resulting in a "532" compound or a = b = 0.20 resulting in a "622" compound. These materials have a laminated crystal structure. The structure is highly related to the MOOH structure. This means that when NMC is immersed in water, some Li will undergo ion exchange with the proton and we refer to it as the "base potential" of NMC. The dissolved Li increases the pH of the water. Depending on the composition of the NMC, its surface area and the amount of water, the ion exchange will maintain equilibrium and consequently raise the pH value.

in reality,

- NMC: The higher the percentage of water,

- Li: M ratio of cathode active material may be high.

- the higher the Ni: Mn ratio of the cathode active material, and

The larger the surface area available for ion exchange,

The base potential of the cathode and the final pH of the aqueous slurry will be higher. The aqueous slurry preparation can be quite difficult because the ratio of cathode to water is very high and consequently the pH of the small amount of water in the slurry becomes very high.

The present invention addresses two major problems that are anticipated from this aspect.

1) Ion exchange of protons and Li causes damage to the cathode material,

2) The high pH of the slurry causes problems in the coating process.

In the aqueous coating process, the cathode material is exposed to water. Water can damage the surface of the cathode product. By monitoring cyclic stability and capacity recovered after storage, the measured calendar life is an important surface property. Thus, aqueous coatings can cause poor cycle stability as well as poor shelf life. The development of an aqueous coating technique that does not deteriorate cycle stability and shelf life is achieved by the present invention.

The aluminum foil is used almost exclusively as a collector for a cathode. Aluminum combines high stability against corrosion with excellent mechanical properties, light weight and high conductivity at high Li voltage. Unfortunately, Al foil is not resistant to corrosion by high pH alkaline solutions. The aqueous based NMC slurry becomes a relatively concentrated alkali LiOH solution, especially when the Ni: Mn ratio in the NMC is high. Even for a few minutes between coating and drying, the aqueous slurry can severely corrode aluminum foil foil. Three methods for solving this problem are (a) increasing the corrosion resistance of aluminum, (b) neutralizing the alkali solution by adding acid to the slurry to lower its corrosiveness, and (c) . Solution (a) is limited to the use of industrial grade aluminum.

The solution (b) focuses on the pH reduction of the aqueous slurry through acid addition. In this way, the slurry can be coated and the aluminum foil is not corroded. However, after adding the acid, the slurry will not reach steady state, the pH will recover and its value will begin to rise again. This "pH recovery" is typical for NMC and will be stronger when the base potential of NMC is higher, for example in the case of higher Ni: Mn NMC. Other cathode materials such as LiCoO ₂ , LiMn ₂ O ₄ based spinel and olivine LiFePO ₄ have lower base potentials and a lower tendency towards pH recovery. The risk of pH recovery necessitates that the slurry be coated immediately. This is very difficult to recognize under mass production conditions where the coating process lasts for several hours. During this time, important properties such as viscosity, degree of dispersion and the like must be stabilized. However, if the pH changes, important properties (depending on the pH) change and the coating process becomes unstable. Any instability such as changes in pH, viscosity, etc. during the coating process will be a serious problem. If the NMC cathode material has a higher base potential, more acid should be added and the pH recovery will become more severe and cause even more severe slurry problems. The present invention therefore provides an NMC cathode material with a lower tendency towards pH recovery when applied to slurries and improved water stability.

With respect to solution (c), different NMC materials are available. NMC triangle with three main areas within the _{(LiNiO 2 - - LiCoO 2 LiNi} 1/2 Mn 1/2 O 2) is of interest.

1: LiCoO ₂ : "LCO" can be prepared in a manner having very low base potential and small pH recovery after acid addition. Therefore, LiCoO ₂ is in principle suitable as a cathode material for aqueous coatings and does not require a reduction in base potential. However, LCO is known to have serious drawbacks. The main drawback is the relative rarity of the Co source relative to the relatively expensive cobalt metal. Even worse, historically, cobalt prices have shown significant fluctuations, and this variation has probably increased the need to find alternatives to LiCoO ₂ . LCO is not a desirable material for use in automotive applications for these and other reasons.

2: Ni: Mn: Mn = 1: NMC: Ni: Mn Almost identical materials are solid, relatively water-stable and have a relatively low base potential. An example of such a cathode material 442 or the NMC 111 (M = Ni Mn _{0 .4 0 .4 0 .2} Co or _{M = Ni 0 .33 Mn 0 .33} Co 0 .33 of Li [Li _{0 .05} M _{0. 95} ] O ₂ ). They are in principle suitable for aqueous coatings and surface treatment to reduce the base potential according to the invention would be helpful but less required.

3: NMC with high Ni: Mn> 1: As the Ni: Mn ratio in NMC increases, the cathode capacity increases and less cobalt addition is required. Therefore, 532 or 622, the cathode materials such as _{(M = Ni 0.5 Mn 0.3 Co} 0.2 or _{Ni 0 .6 Mn 0 .2 Co 0} .2 of LiMO _2, which may be doped) are combined with a relatively low material cost and high capacity . They guarantee a low cost per Ah of the final battery capacity (Ampere hour). For this reason it would be very beneficial if the above advantages could be used for automotive applications. However, since Ni: Mn dramatically increases the base potential, applying a high Ni NMC cathode material to an aqueous electrode coating would be very difficult at first glance. This problem is solved by the present invention.

Of particular interest in the automotive industry is NMC cathode materials with "intermediate and high" NMCs such as 532 with 1 <Ni: Mn <4, more specifically 1.2 <Ni: Mn? These cathode materials are currently used in inexpensive batteries due to their low cost capacity per Ah. Cost competition is so severe that cost reduction using an aqueous coating process is also important for inexpensive applications. At the same time, a heavy phase NMC cathode, such as 532, has a prospect of aqueous coating because the reduction in base content needed in the slurry is limited, and a slight reduction in base content and an improvement in water stability may be sufficient to enable successful aqueous coatings have. For these materials, the present invention is particularly interesting.

Another aspect of the invention is the stability of the slurry dispersion. Industrial coating operations require that the slurry be evenly dispersed throughout the coating process. Depending on the surface charge of the solid component including the cathode powder and conventional carbon additive in the solvent, the dispersion may be stable or have a tendency to agglomerate. Usually, the pH region is in a stable dispersion, but the slurry may become unstable when the pH changes. In order to achieve a stable slurry, it is desirable to limit the base potential of the cathode powder. The present invention provides a NMC cathode that interacts less with water to more freely adjust the pH of the slurry in a manner that stabilizes dispersion and avoids agglomeration.

When applying conventional organic NMP / PVDF based coatings, the electrode active material could be partially coated with a PVDF binder. The PVDF coating in the battery will become conductive to Li ions as it swells in the electrolyte. Similarly, after the aqueous coating, when using a CMC thickener, the electroactive cathode material after drying may be partially or fully coated with CMC. However, contrary to PVDF, CMC does not swell in the electrolyte and tends to produce a surface layer with low Li ion conductivity. This layer causes an increase in DCR resistance. The present invention addresses the development of aqueous coating techniques that result in low DCR resistance as a major theme and reduces the increase in DCR during battery operation. The present invention teaches that the presence of a polymeric surface that is capable of swelling in the electrolyte creates an additional diffusion path that can reduce DC resistance.

In addition, when applying an NMP / PVDF based coating, the cathode particles are bonded by a flexible polymer that allows some elasticity. For aqueous coatings, the elasticity is provided by the addition of rubber particles (SBR for the anode). In the case of the cathode of the present invention, fluorinated acrylic latex (FAP) rubber is used. The preliminary data reveal that stability is not sufficient to overcome under abuse conditions, even though the stability of the cathode state (under high Li voltage) increases. The development of a more elastic cathode material makes it possible to lower the required amount of latex, thus reducing the swelling.

As mentioned earlier, in order to avoid aluminum corrosion and improve slurry stability, there is a need for a cathode material having a high capacity but low base content, which appears to be a contradiction. By having a hydrophobic surface, higher water stability is assured. The elastic polymer surface membrane provided in the present invention ensures the mechanical properties of a more excellent electrode, Reduction in brittleness is expected. If the surface film swells in the electrolyte, the present inventors can expect higher rate characteristics and lower DCR resistance.

Details of the experiment

1) Coating

The organic NMP substrate coating process is described in Example 1. The aqueous coating process is described in Example 2.

2) Full cell assembly

For the purpose of a full battery test, the prepared anode (cathode) is assembled with a cathode (anode), which is a typical graphitic carbon, and a porous electrically insulating film (separator). The whole cell is manufactured by packaging the following major steps: (a) electrode slitting (b) electrode drying (c) jellyroll winding (d) packaging.

(a) Electrode cutting: After NMP or aqueous coating, the electrode active material can be cut with a slitting machine. The width and length of the electrodes depend on the battery application.

(b) With tap: There are two types of tabs. The aluminum tab is attached to the anode (cathode), and the copper tab is attached to the cathode (anode).

(c) Electrode drying: The prepared positive electrode (cathode) and negative electrode (anode) were dried in a vacuum oven at 85 ° C to 120 ° C for 8 hours.

(d) Jelly roll winding: After drying the electrode, the jelly roll is manufactured using a winding machine. The jelly roll comprises at least a cathode (anode), a porous electrically insulating film (separator) and a cathode (cathode).

(e) Packing: The jelly rolls produced are contained in an aluminum laminate membrane package in an 800 mAh cell, resulting in a pouch battery. In addition, jelly rolls are impregnated with electrolytes. The amount of electrolyte is calculated according to the porosity and size of the anode and cathode, and the porous separator. Finally, the packed complete battery is sealed by a sealer.

3) Evaluation of complete battery

It is possible to carry out the evaluation test of a number of various complete batteries. The present invention shows the results for (a) cycle stability, (b) capacity and rate characteristics, (c) swelling, (d) storage test and (e) DCR resistance test.

(a) Cycle stability: The battery is fully charged and discharged for several hundred cycles. The cycling test is carried out at 25 DEG C or at an elevated temperature (e.g., 45 DEG C) which accelerates undesired side reactions, thus leading to a faster loss of capacity. In the case of an aqueous coating, the present inventors could expect that exposure to water could damage the cathode. Damaged cathodes could negatively impact cycle stability at elevated temperatures.

(b) Capacity and rate-limiting characteristics: Capacitance is a discharge capacity measured at a rate of 0.1 C rate (C rate) at 4.3 V to 2.7 V. The rate-limiting characteristic is the discharge capacity at 0.5, 1.0, 2.0, 3.0, and 4.0 C rates expressed as a percentage of 0.2 C rate. 0.2C corresponds to the electric current discharging the charged battery within 5 hours. Lt; RTI ID = 0.0 &gt; 0.2C &lt; / RTI &gt; current.

(c) Swelling: The pouch battery is fully charged and inserted into an oven heated to 90 ° C and kept at the same temperature for several hours. The cathode charged at 90 캜 reacts with the electrolyte and generates gas. The generated gas produces swelling. In the Examples, the inventors report values for an increase in thickness (= swell) measured after 4 hours of high temperature exposure. Swelling is a problem for many applications and besides, the authors think that swelling is a very sensitive way to detect the ultimate surface damage from exposure to water in the coating process.

(d) Storage test, ie, residual and recovery capacity: The battery is fully charged and stored at 60 ° C for 1 month. After one month, remove the battery from the 60 ° C chamber and test at 25 ° C. The battery is discharged, and the remaining capacity is measured in the discharging process. After recharging, the battery is discharged and recovery capacity is obtained. After this capacity is confirmed, the battery is stored at 60 ° C for a further 1 month, and the residual capacity and recovery capacity are measured again. The battery is stored again for one month, and the battery is measured again. In addition to its relevance to many applications, storage experiments are also a very sensitive means of assessing the damage of the cathode in the aqueous coating process.

(e) DCR resistance test connected with the storage test: After storing for 1, 2, and 3 months at 60 ° C, measure the DCR resistance of the battery in addition to the capacity measurement.

The DCR resistance is derived from the voltage response to the current pulse, and the procedure used is in accordance with the United States Advanced Battery Consortium LLC (USABC) standard. The DCR resistance is very suitable for application because the data can be used to estimate future fade rates to diagnose battery life, and the DCR resistance is further enhanced by the fact that the reaction product of the reaction between the electrolyte and the anode or cathode is a low conductive surface layer, Which is very sensitive to detecting damage to the electrode.

In all experiments, so-called NMC532 (NMC with a metal composition M = Ni _0.5 Mn _0.3 Co _0.2 in Li _1.03 M _0.97 O ₂ ) was used as the cathode material. NMC532 is a relatively inexpensive cathode material, with a heavy base content. NMC532 has a relatively high capacity of about 170 mAh / g at 4.3 V when tested at 0.1 C rate. NMCs with lower Ni content are usually lower in base content, thus making aqueous coatings much easier. However, the cathode material (such as NMC111) containing a lower base content tends to also have a reversible capacity. Therefore, NMC532 is a good compromise with low metal cost, coating possibilities by aqueous process and high capacity to allow. The present invention will be illustrated in the following examples.

Example 1

Example 1 demonstrates how much the aqueous coating results in a change compared to a conventional NMP based coating. The different steps used in the aqueous coating process and the effect of the chemical (e.g., the effect of the CMC binder or the effect of exposure to water). This is done by manufacturing different cathode materials, all from the same type of precursor, which is a mass produced NMC532 powder. The cathode material is then coated using a conventional organic NMP substrate coating process and the entire pouch cell is assembled. The choice of chemicals, the amount of chemicals added and the process conditions are chosen to simulate a conventional aqueous coating. Table 1.1 shows the experimental design.

<Table 1.1>

Sample list of NMC532 coated with aqueous binder component

Preparation of NMC532 Samples

1A) Manufacturing of NMC532

Standard NMC532 was prepared by the following steps in a mass production line of Umicore (Korea). (a) mixing of lithium and nickel-manganese-cobalt precursors; (b) synthesis in an oxidizing atmosphere; and (c) milling. Details of each step are as follows.

Step (a): Mixing lithium and nickel-manganese-cobalt precursors using a dry powder mixing process. Put the precursor into the container. Lithium carbonate and mixed Ni-Mn-Co oxyhydroxide are used as lithium and Ni-Mn-Co precursors. The precursors are mixed in a vertical single shaft mixer by a dry powder mixing process.

Step (b): sintering in an oxidizing atmosphere. The powder mixture obtained from step (a) is sintered in a tunnel of an oxidizing atmosphere. The sintering temperature is > 900 DEG C and the residence time is ~ 10 hours. Dry air is used as the oxidizing gas.

Step (c): After sintering, the sample is finally milled in a mill.

1B) Preparation of NMC532 exposed to water

Example 1B is prepared and the effect on exposure to water is investigated. Exposure to water is similar to slurry preparation followed by drying in an aqueous coating process. The powder used for exposure to water is of the same MP grade and is virtually identical to Sample 1A.

Example IB is prepared by the following main steps. (a) immersing the MP powder sample in water and (b) drying.

A detailed description of each step is as follows.

Step (a): 1.3 kg of MP NMC532 sample and 390 ml of H ₂ O are added to the beaker. The mixture is stirred for 1 hour at 200 rpm using an overhead stirrer.

Step (b): Drying: A mixture of lithium nickel-manganese-cobalt oxide and water in slurry form is dried in a convection oven at 150 占 폚 for 15 hours.

1C) Preparation of NMC532 exposed to water and FAP added

Example 1C is prepared to investigate the effect of exposure to water with addition of a FAP binder. Exposure is associated with slurry preparation followed by drying of the aqueous coating process. The powders used are of the same MP grade and in effect identical to Sample 1A.

Example 1C is prepared by the following main steps. (a) wet mixing of the aqueous binder component (1%) and water with NMC532 (99%); (b) drying and (c) grinding.

A detailed description of each step is as follows.

Step (a): 2 kg of NMC532 sample is mixed with water (600 ml) and 40.4 g of a 50 wt% FAP binder aqueous dispersion is added. The mixture is stirred for 1 hour at 600 rpm using an overhead stirrer.

Step (b): Drying: The slurry is dried in a convection oven at 150 DEG C for 20 hours.

Step (c): After drying, finally, the sample is pulverized by a pulverizer.

1D) Preparation of NMC532 exposed to water and CMC added

Example 1D is prepared to investigate the effect of exposure to water with the addition of CMC (a binder that changes viscosity). Exposure is associated with slurry preparation followed by drying of the aqueous coating process. The powders used are of the same MP grade and are virtually identical to Sample 1A.

Example 1D is prepared by the following main steps. (a) wet mixing of CMC (1 wt%) and water with NMC532 (99 wt%) (b) drying and (c) grinding.

A detailed description of each step is as follows.

Step (a): 2 kg of NMC532 sample are mixed with water (100 ml) and 1030 g of a 2 wt% aqueous solution of CMC are added. The mixture is stirred for 1 hour at 600 rpm using an overhead stirrer.

Step (b): Drying: The slurry is dried in a convection oven at 150 DEG C for 20 hours.

Step (c): After drying, finally, the sample is pulverized by a pulverizer.

1E) Preparation of NMC532 exposed to water and with binder CMC and FAP added

Example 1E is prepared to investigate the effect of exposure to water with both FAP and CMC as binder components. Exposure is similar to slurry preparation followed by drying of the aqueous coating process. The powders used are of the same MP grade and are virtually identical to Sample 1A.

Example 1E is prepared by the following main steps. (a) wet mixing of the aqueous binder component (1 + 1%) and water with NMC532 (98%) (b) drying and (c) grinding.

A detailed description of each step is as follows.

Step (a): 1.3 kg of NMC532 sample is mixed with water (50 ml) and 663 g of 1 wt% CMC aqueous solution and 26.5 g of 50 wt% FAP water dispersion. The mixture is stirred for 1 hour at 140 rpm using an overhead stirrer.

Step (b): Drying: The slurry is dried in a convection oven at 150 DEG C for 20 hours.

Step (c): After drying, finally, the sample is pulverized by a pulverizer.

Slurry manufacturing and coating

The slurry was prepared by mixing 700 grams of NMC532 of Example 1A (exposed sample of Example 1B-1E) with NMP, 7.29 grams of graphite, 7.29 grams of SuperP® (conductive carbon black from Timcal) and 145.8 grams of NMP solution Lt; RTI ID = 0.0 &gt; 10 wt% &lt; / RTI &gt; PVDF substrate binder. The mixture is mixed in a planetary mixer for 2.5 hours. In the mixing process, additional NMP is added. The mixture is transferred to a dispersing mixer and mixed for 1.5 hours with the addition of additional NMP. A typical total amount of NMP used is 230 g. The final solids content in the slurry is about 70 wt%.

Transfer the slurry to the coating line. A double coated electrode is prepared.

The electrodes are irradiated with a naked eye and examined under a microscope. No pinhole is detected at all, and no trace of alumina corrosion is detected. The electrode surface is smooth. The electrode loading is 1.6.1 g / cm &lt; ^{2 &} gt ;. The electrode is pressed with a roll press to achieve an electrode density of about 3.2 g / cm &lt; ³ &gt;. Electrode is used to manufacture a pouch-type full battery as described above.

Result of full battery test

Tables 1.2 to 1.7 list the detailed results of the full battery test. [Figure 1a] - [Figure 1f] show data of a table in the figure. Table 1.2 shows the results of the reversible capacity and rate performance tested at 25 ° C. The reversible capacity is based on the weight of the treated sample and includes the weight of the aqueous binder component and excludes the weight of the carbon additive and PVDF from the NMP based coating. Figure 1 A summarizes the results in Table 1.2.

Table 1.3 shows the temperature characteristics of the performance range at -20 캜 to 60 캜. The data in the table is expressed as a percent capacity obtained by immersing the fully charged battery (at 25 캜) in a temperature chamber and measuring the discharge capacity at 0.5 C after temperature equilibration. Figure 1b summarizes the results in Table 1.3.

Table 1.4 shows the results of the swelling test. A fully charged cell is placed in a preheated oven at 90 占 폚, held at 90 占 폚 for 4 hours, and the thickness is measured and compared to the initial cell thickness.

Table 1.5 shows DCR (DCR = DC resistance). The DC resistance is calculated according to the USABC procedure for pulse testing. The pulse is a 1C rate for 10 seconds. Figures 1C and 1D summarize the data in Table 1.5.

Tables 1.6 and 1.7 show storage results at 60 占 폚 for 3 months. Table 1.6 shows the recovery capacity. Table 1.7 shows the storage capacity. Place two fully charged cells in a chamber heated to 60 ° C. After one month, the battery is discharged, the battery is discharged at 25 DEG C (the storage capacity is calculated), the battery is recharged and discharged, and the recovery capacity is calculated by the secondary discharge. The charge / discharge cycle is executed at a rate of 1C / 1C. Then, the battery is recharged and storage is continued, and recovery and retention data are measured after 2 months. Repeat after 3 months. Figures 1E and 1F summarize the data obtained.

Finally, [Fig. Ig] and [Fig. 1h] show cycle stability at 25 ° C or 45 ° C. The figure shows the discharge capacity ratio (compared to the initial discharge capacity at 1C discharge rate) in the 1C / 1C charge / discharge cycling process, with each 50th cycle at a slower rate (1C / 0.2C charge / discharge).

Obviously, exposure to water and addition of chemicals used in aqueous coatings will change battery performance. In most cases, performance is poor. Surprisingly, however, cells with cathodes containing all the chemicals required for aqueous coatings (1% CMC + 1% FAP, exposed to water) exhibit excellent overall performance. Capacity and rate performance are similar to standards, DCR and storage properties are better, cycle stability is similar or slightly worse, and swelling is almost similar. Example 1 makes it possible to conclude that aqueous coating is possible and that the chemicals used in aqueous coatings are suitable for full cells and that eventually exposure to the required water does not dramatically deteriorate the cells.

<Table 1.2>

Capacity and rate-response characteristics of NMC532 coated with aqueous binder (NMP-based binder full battery)

<Table 1.3>

Results of temperature characteristics of NMC532 coated with aqueous binder (NMP-based binder full battery)

<Table 1.4>

Swelling results of NMC532 coated with aqueous binder (NMP substrate binder full cell)

<Table 1.5>

DCR, DCR increase (NMP-based binder full battery) of NMC532 coated with aqueous binder

<Table 1.6>

Recovery Capacity of NMC532 Coated with Aqueous Binder (NMP Base Binder Complete Battery)

<Table 1.7>

Storage capacity of NMC532 coated with aqueous binder (NMP-based binder full battery)

Example 2

This example will compare the performance of a complete cell comprising an anode (Example 2B) produced by an aqueous coating process as compared to a conventional electrode (Example 2A) resulting from an NMP + PVDF based coating process. As in Example 1, NMC532 (NMC with metal composition M = Ni _0.5 Mn _0.3 Co _0.2 ) was used as the cathode material, the material of Example 2A was the same as Example 1A, and the material of Example 2B was the same MP And substantially the same powder as Sample 1A was used. A conventional electrode is prepared as described in Example 1. [

For aqueous slurry preparation and electrode coating, the slurry was mixed with 96 wt% NMC532 powder, 1.5 wt% Super-P and 1 wt% graphite as a conductive agent, 0.7 wt% carboxymethyl cellulose (CMC) as an aqueous base binder, 1 wt% of a fluorine acrylate polymer (FAP) is mixed into the mixture. The mixing procedure is divided into two steps. The first step is slow rate mixing for about 2.5 hours using a rotating-flow mixer. The rate of the first mixing step is about 100 rpm. The second stage is high-speed mixing for about 1 hour using a dispersion mixer. The speed of the second stage is about 4000 rpm.

The prepared slurry is coated on an aluminum foil in a coater. The electrodes are manufactured with a fixed loading weight, length and width. The coating temperature was 60 캜 (inside the machine). After coating, the electrode is pressed with a pressing machine to obtain an electrode density of 3.2 g / cm ³ . The prepared electrode is dried in a vacuum oven at 85 DEG C for 8 hours.

Electrochemical tests: Table 2.1 - Table 2.4 summarizes the results of the electrochemical characteristics of the cell. [Figure 2a] - [Figure 2g] shows the data of the table.

Table 2.1 and [Figure 2a] show the reversible capacity and rate performance tested at 25 ° C. NMC532 has a similar capacity in an NMP based binder system and an aqueous binder system.

Table 2.2 shows DCR (DCR = DC resistance). The DC resistance is calculated according to the USABC procedure for pulse testing. The pulse is a 1C rate for 10 seconds. Figures 2b and 2c summarize the data in Table 2.

Table 2.3 and Table 2.4 show storage results for 3 months at 60 ° C. Table 2.3 shows the recovery capacity, and Table 2.4 shows the storage capacity. The test protocol is the same as in Example 1.

In the high temperature storage test procedure, the DCR and DCR increase of NMC532 in aqueous binder systems is superior to that of NMC532 in organic NMP based binder systems. For retention capacity and recovery capacity, the NMC532 sample in the aqueous binder system shows comparable results to the NMC532 in the NMP substrate binder system.

Finally, [Figure 2f] and [Figure 2g] show cycle stability at 25 ° C and 45 ° C, respectively. The figure shows the discharge capacity ratio (compared to the initial discharge capacity at 1C discharge rate) in 1C / 1C charge / discharge cycling, with each 50th cycle at a slower rate (1C / 0.2C charge / discharge). The cell stability at room temperature of the cell with an aqueous electrode is somewhat superior to that of the NMP based binder system. A cell with an aqueous coated electrode at elevated T (45 DEG C) certainly exhibits excellent results. It can be summarized that an aqueous coating technique can be applied to NMC compounds for automotive applications. For the NMC532 product, the aqueous binder system is slightly lower, but still has acceptable rate-limiting performance. The aqueous coatings exhibit advantages over conventional coatings for high temperature storage tests (DCR, DCR increase) and cycle stability, especially cycle stability at elevated temperatures of 45 &lt; 0 &gt; C.

<Table 2.1>

 Capacity and rate-response characteristics of NMC532 in NMP substrate binder system and aqueous binder system

<Table 2.2>

DCR, DCR increase of NMC532 in NMP substrate binder system and aqueous binder system

<Table 2.3>

The storage capacity of NMC532 in the NMP substrate binder system and the aqueous binder system

<Table 2.4>

Recovery capacity of NMC532 in NMP substrate binder system and aqueous binder system

Example 3

In this example, the aqueous preparation of Example 2B (= 3B1) is repeated to confirm reproducibility. The embodiment compares the results of the second full battery 3B2 with the results of 3B1. The example demonstrates that the results of Example 2 are reproducible. Additional properties such as swelling or low temperature performance are measured. Table 3.1 - Table 3.6 summarizes the test results. [Figure 3a] - [Figure 3h] show table data. The following criteria are used in [Figure 3a] - [Figure 3g].

Table 3.1 shows the reversible capacity and rate performance tested at 25 ° C. Figure 3A summarizes the results of Table 1. Example 3B2 shows a similar capacity to Example 3B1.

Table 3.2 and Table 3.3 show the results of a full cell (Example 3B2) containing a positive electrode prepared by an aqueous coating process on a conventional electrode (same as Example 3A, Example 1A) resulting from the NMP + PVDF substrate coating process ). Table 3.2 shows the temperature characteristics in the performance range at -20 캜 to 60 캜. The data in the table is expressed as a percent capacity obtained by immersing the fully charged battery (at 25 캜) in a temperature chamber and measuring the discharge capacity at 0.5 C after temperature equilibration. Figure 3b summarizes the results in Table 3.2. It is clear that a cell with an aqueous cathode can not match the low temperature characteristics of the cell with the NMP substrate binder system, although the result is not unacceptable. Table 3.3 shows the results of the swelling test. A fully charged cell is placed in a preheated oven at 90 占 폚, held at 90 占 폚 for 4 hours, and the thickness is measured and compared to the initial cell thickness. The swell characteristics of NMC532 in the aqueous binder system (Example 3B2) are worse than the NMP substrate binder system (Example 3A).

Table 3.4 shows DCR (DCR = DC resistance). The DC resistance is calculated according to the USABC procedure for pulse testing. The pulse is 1C for 10 seconds. [Figure 3c] and [Figure 3d] summarize the data in Table 3.4.

Tables 3.5 and 3.6 show storage results at 60 ° C for 3 months. Table 3.5 shows the storage capacity, and Table 3.6 shows the recovery capacity [Fig. 3e] and [Fig. 3f] summarize the data obtained. Example 3B2 shows similar or slightly improved results compared to Example 3B1. Finally, [Figure 3g] and [Figure 3h] show cycle stability at 25 ° C or 45 ° C. The protocol is the same as in Example 2, and the results are reproducible.

It can be summarized that aqueous coating techniques can be applied and reproducible results. Example 3B2 confirms the results of Example 3B1. In particular, Example 3B2 confirms that aqueous coatings exhibit lower rate-of-control properties but lower DCR, better storage properties and better cycle life. In addition, it can be concluded that the application of an aqueous coating, in particular the swelling and rate performance as well as the low T performance, should still be improved.

<Table 3.1>

Capacity and rate characteristics of NMP substrate binder system and aqueous binder system

<Table 3.2>

Temperature characteristics of NMP substrate binder system and aqueous binder system

<Table 3.3>

Swelling properties of NMP substrate binder system and aqueous binder system

<Table 3.4>

Increased DCR, DCR of NMP substrate binder system and aqueous binder system

<Table 3.5>

The storage capacity of the NMP substrate binder system and the aqueous binder system

<Table 3.6>

Recovery capacity of NMP substrate binder system and aqueous binder system

Example 4

This example discloses the preparation of a dual shell coated NMC as described in WO2011 / 054440. The dual shell coated NMC has an internal shell of LiF. LiF is the reaction product of a fluorinated polymer with a soluble base present on the surface of the uncoated material. Due to the consumption of the surface base, the overall base content (as measured by pH titration) is low. Lower base content causes less swelling than uncoated NMC. The outer shell is a hydrophobic polymer. In the aqueous slurry preparation process, the outer polymer shell protects at least a portion of the NMC surface from exposure to water. After assembling the battery, the hydrophobic polymer expands in the electrolyte and the surface becomes ionic conductive.

In an embodiment, the dual shell NMC532 is prepared by the following main steps. (a) mixing a lithium Ni-Mn-Co oxide with a fluorine-containing polymer precursor and (b) calcining in an oxidizing atmosphere. A detailed description of each step is as follows.

Step (a): Mixture of lithium Ni-Mn-Co oxide and fluorine precursor using a dry powder mixing process. Put the precursor into the container. 1 wt% of fine powdered PVDF-HFP (= polyvinylidene fluoride-hexafluoropropene) copolymer is used as the fluorinated polymer precursor. Lithium Ni-Mn-Co oxide and fluorine precursors are mixed by a dry powder mixing process in a vertical single-shaft mixer.

Step (b): sintering in an oxidizing atmosphere. The double-shell NMC532 sample is calcined using the mixture of step (a) in a chamber of an oxidizing atmosphere or in a channel furnace. In this embodiment, the sintering temperature is 250 DEG C and the residence time is 5 hours. The calcination takes place in a drying air stream which is used as an oxidizing gas. [Figure 4] shows an FESEM micrograph of a Li Ni-Mn-Co oxide / 1% PVDF mixture heated to 250 ° C.

Two samples (4B & 4D) are prepared from two different NMC532 precursor samples (4A & 4C) according to steps (a) and (b). 4A is a precursor sample that is approximately the same mass-produced material as Example 1A, and 4C is an NMC532 sample of the pilot line and has a higher soluble base content than normal mass production. Table 4.1 summarizes the history of the samples. Soluble bases are measured by pH titration. To measure the pH, 7.5 g of the sample is immersed in 100 ml of water. The surface impurities such as Li ₂ CO ₃ and LiOH are dissolved while stirring. In addition, an ion exchange reaction occurs in which Li + (solid) and H + (water) are exchanged. After stirring for 10 minutes, a transparent liquid is obtained by filtration. The base content in the liquid is obtained by pH titration until pH = 4.5. The value is reported in μmol per g of cathode material. After double shell coating, the total base is compared with the value before coating to confirm that the soluble base content is reduced by 22-25%.

<Table 4.1>

Example 5

Example 5 shows that dual shell coatings result in lower pH recovery. NMCs with higher Ni content have higher capacity but higher soluble base content. Soluble bases cause serious problems because they severely corrode aluminum foil foil. The start of aluminum foil corrosion can be easily detected by observing the pinhole. These pinholes are still derived from hydrogen gas evolution when wet and warm, and as the drying progresses, the base coat layer attacks the aluminum foil.

To prevent aluminum corrosion, the pH of the coating slurry is reduced by acid addition. In this example, 0.05 wt% of H ₂ SO ₄ (in wt% of active NMC) was added to reduce the pH.

To illustrate the mass production, NMC532 was used for slurry preparation as in Example 1A. The aqueous slurry was prepared analogously to Example 2 except that no sulfuric acid was added. After coating, the electrodes were visually inspected.

In addition, the electrodes were inspected with a SEM microscope (not compressed with a roll press) - see left picture of FIG. 5a. The electrode shows damage - pin holes appear. The pinhole is derived from hydrogen generation after the base attacks aluminum. In some cases, damage to the alumina foil can be found. Apparently, aluminum corrosion has occurred. SEM micrographs of the coated electrode, right photo of Figure 5a, show the results of acid addition. Al corrosion is prevented, there is no pinhole, and the electrode surface is smooth.

A serious problem is pH recovery. The pH is reduced immediately after the acid addition, but is gradually restored due to the ion exchange reaction between the water and the external surface of the bulk. The changing pH changes the slurry properties in the coating process, causing process stability problems in mass production and eventually causing aluminum corrosion, which is highly undesirable.

In this example, pH recovery is investigated after addition of acid to NMC532 and double shell coated NMC532. 150 g of the sample is immersed in 75 ml of water. Record the pH every 3 seconds. The pH is stabilized after 13 minutes. 1.42 ml of 10% H ₂ SO ₄ (dilute 1-fold volume of concentrated H ₂ SO ₄ with water to make 10-fold volume) is added. The pH drops immediately, after which the pH is continuously restored. Two sets of samples were examined. Table 5.1 summarizes the samples and the results. Figure 5b details the results. 5A is the reference MNC532 and is the same as 4A. 5B is the same material after dual shell coating and is the same as 4B. 5C (= 4C) is the NMC532 base material with higher base content and 5D (= 4D) is the NMC532 double shell coated material with higher base content. We observe that the double shell coated NMC532 has a lower pH than the reference not normally coated. As expected, the high base NMC (5C) showed a high pH before the addition of acid and a high pH recovered. When using high base NMC after double shell coating, the same amount of acid causes significantly lower pH (see 5D).

The application of dual shell coated NMCs is possible to reduce aluminum corrosion, and in this way the aqueous coating technology can be pushed to a higher capacity NMC because the higher the volume, the higher the base content is usually accompanied .

<Table 5.1> Sample summary

Example 6

This example shows a comparison of a dual shell coated NMC with a reference NMOC in an aqueous binder system. Normal NMC and double-shell coated NMC are tested as cathode materials in wounded pouch-type full cells. In this battery, the anode is obtained by an aqueous coating technique. This example compares the performance of standards with the performance of dual shell coated NMC. In this example, the reference sample was also a precursor for the dual shell coating process. Example 6A is the standard and is the same material as in Example 3B2. Briefly, the center of the reference NMC and the double shell coated NMC are the same. Table 6.1 gives an overview of the samples used. Electrochemical test results are summarized in Tables 6.2 to 6.7 (Tables 6.2 & 6.3: Coating Type is an aqueous binder system). 6A to 6H show data of a table.

<Table 6.1>

Complete cell information from an aqueous coated electrode

Table 6.2 and [Figure 6a] show the results of capacity and rate performance. Table 6.3 and [Figure 6B] show the temperature characteristics. The dual shell NMC532 has a slightly lower capacity and lower rate performance than the NMC532 reference sample in a full battery test of an aqueous binder system. Dual shell NMC532 and reference NMC532 have similar temperature characteristics in a full battery test of an aqueous binder system. A slightly lost capacity and a slightly lower rate-response characteristic can be explained by the presence of a double shell that does not contribute to the reversible capacity and serves as an additional resistive layer. Table 6.4 shows the results of the swelling test. The performance of the dual shell coated NMC is similar to the reference performance. Table 6.5 and [Figure 6c] and [Figure 6d] show the DCR increase in the initial DCR and storage process. Double shell coated NMC shows excellent performance. Dual shell coated NMCs have (a) lower initial DCR and (b) much lower growth rates.

Table 6.6 and Table 6.7 and [Figure 6e] show performance after storage. Double shell coated NMC exhibits excellent storage properties. This has the highest retention of recovered capacity.

Finally, [Figure 6g] and [Figure 6h] show the results of cycle stability. At 25 degrees C, double-shell coated NMC exhibits significantly improved cycle stability, and even at 45 DEG C dual shell coated NMC has better performance compared to the results for the NMC standard.

When applied by an aqueous coating technique, the dual shell coated NMC can be summarized as exhibiting similar, slightly better, or significantly improved performance as compared to the NMC standard in general. The reduction of DCR and the reduction of DCR increase during operation are particularly important for automotive applications that require high pulse power. Since automotive batteries must last for a long time, high cycle stability and a stable recovery capacity in the storage process are required. Obviously, dual shell coated NMC532 compared to uncoated NMC532 exhibits lower DCR, less DCR reduction, less loss of recovery capacity and significantly improved cycle stability. This makes the invention particularly suitable for automotive applications.

<Table 6.2>

Capacity and rate-response characteristics of NMC532 and dual-shell NMC532 (aqueous binder full battery)

<Table 6.3>

Temperature characteristics of NMC532 and dual shell NMC532 (aqueous binder full battery)

<Table 6.4>

Swelling properties of NMC532 and dual shell NMC532 (aqueous binder full cell)

<Table 6.5>

DCR, DCR increase of NMC532 and dual shell NMC532 (aqueous binder full battery)

<Table 6.6>

Storage capacity of NMC532 and dual shell NMC532 (aqueous binder full battery)

<Table 6.7>

Recovery capacity of NMC532 and dual shell NMC532 (aqueous binder full battery)

Claims (15)

An aqueous lithium ion battery cathode slurry comprising a cathode active material comprising a lithium transition metal oxide powder, wherein the lithium transition metal oxide powder comprises an aggregate of primary particles, wherein the primary particles comprise a coating layer comprising a polymer Aqueous lithium ion battery cathode slurry. The aqueous lithium ion battery cathode slurry of claim 1, wherein the coating layer is hydrophobic. 3. The aqueous lithium ion battery cathode slurry of claim 1 or 2, wherein the polymer is a fluorine-containing polymer comprising 50 wt% or more of fluorine. 4. The method of claim 3, wherein the coating comprises a first coating inner layer and a second coating outer layer, the second outer layer comprises a fluorine containing polymer, the first inner layer comprises a reaction product of a fluorine containing polymer and a primary particle surface Lt; RTI ID = 0.0 &gt; Li-ion &lt; / RTI &gt; 5. The aqueous lithium ion battery cathode slurry of claim 4, wherein the reaction product comprises LiF.  6. The aqueous lithium ion battery cathode slurry of claim 5, wherein lithium in LiF originates from a primary particle surface. 7. The aqueous lithium ion battery cathode slurry of claim 5 or 6 wherein the fluorine in the reaction product comprising LiF is from a partially degraded fluorine-containing polymer present in the second outer layer. 7. An aqueous lithium ion battery according to any one of claims 4 to 6, wherein the first coating inner layer consists of a LiF film having a thickness of at least 0.5 nm, preferably at least 0.8 nm, most preferably at least 1 nm. Cathode slurry. The method of claim 1, wherein the lithium transition metal oxide of the general formula Li _{1 + a} M _{1 -} a M _a O _{2 ± b} 'with _k S _m, and said general formula -0.03 <a <0.06, b < 0.02, M Wherein at least 95% of M consists of one or more elements from the group of Ni, Mn, Co, Mg and Ti, M 'is at least one element selected from the group consisting of Ca, Sr, Y, La, Ce and Zr Wherein 0? K? 0.1, where k is expressed in wt% and 0? M? 0.6, wherein m is expressed in mol%. The aqueous lithium ion battery of claim 9, wherein M = Ni _x Mn _y Co _z wherein x> 0, y> 0, z> 0, x + y + z = 1 and x / Cathode slurry. 11. The aqueous lithium ion battery cathode slurry of claim 10, wherein 0.33? X? 0.7 and 0.1 <z <0.35. 11. The aqueous lithium ion battery cathode slurry of claim 10, wherein 0.4? X? 0.6 and x / y> The fluorine-containing polymer according to claim 3, wherein the fluorine-containing polymer is one of PVDF, PVDF-HFP or PTFE, and the fluorine-containing polymer is preferably composed of agglomerated primary particles having an average particle size of from 0.2 μm to 0.5 μm In aqueous lithium ion battery cathode slurry. The use of the aqueous lithium ion battery cathode slurry of claim 1 in the manufacture of a cathode for a lithium ion battery, wherein said cathode comprises an aluminum substrate. Use of the aqueous lithium ion battery cathode slurry of claim 1 in the manufacture of a lithium ion battery for automotive applications.

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